The invention relates to a filter device having two flow spaces, of which a first space, preferably a permeate space, is formed by the tubular or capillary tube passages of a hollow-fiber bundle poured at its ends into a molding compound, and a second space, preferably a filtrate space, is formed by a housing enclosing the fiber bundle, the first space being sealed off by caps, placed on the molding compounds, with sealing devices running over the peripheral areas of said molding compounds, and the molding compounds being braced against the housing.
The German laid open print 26 46 358 discloses a filter device in which the hollow-fiber bundle encloses a central conduit in a ring-like manner, and the ends of the ring-shaped hollow-fiber bundle are sealed off by a molding compound both with respect to the central conduit and with respect to the housing casing concentrically enclosing it.
Another known filter device likewise comprises a tubular housing which encloses the hollow-fiber bundle, the ends of the hollow-fiber bundle being joined to the ends of the tubular housing by a molding compound. In this filter device, the housing is provided in each case with radial connection pieces, adjacent to the molding compounds, which form the inlets and outlets to the second flow space. The capillary tubes of the hollow-fiber bundle enclosed by the molding compounds are cut at their end faces to open them. Caps provided with connection pieces which form the inlets and outlets of the first flow space are then placed sealingly on the ends of the tubular casing.
These known filter devices are used, for example, as capillary dialyzers, the flow spaces formed by the capillary-tube passages forming the blood chamber, and the housing enclosing the hollow-fiber bundle forming the dialysate chamber in which the dialysate flows around the hollow fibers.
The problem existing in the known filter devices is that the molding compound, usually made of PU (polyurethane), which hardens in a disk shape and forms a sealing between the two flow spaces, shrinks when hardening, so that stresses develop in the disk-shaped sealings formed by the molding compounds which can lead to cracks and even detachments of the molding compounds from the housing casing enclosing them. As a result, the two flow spaces are no longer completely sealed off from one another, and the adhesion of the sealing compounds to the housing enclosing the fiber bundle, said adhesion producing the seal, is no longer reliably assured.
In a filter device of the type indicated at the outset disclosed by EP 0 305 687 B1, the disk-shaped molding compounds are enclosed by interposed rings to which the molding compounds do not adhere, so that they can shrink free of stress. This stress-free shrinking prevents cracks in the disk-shaped molding compounds, and makes it possible to dispense with a direct sealing between the peripheral edge of the sealing compounds and the housing enclosing them. To nevertheless maintain a sealing between the two flow spaces, the first space is sealed off by caps placed on the molding compound, and specifically by sealing devices which run over the edge area of the molding compound and against which the caps are pressed.
In this known filter device, the problem now exists of producing a connection to the second space formed by the housing enclosing the fiber bundle. This connection is produced in the known filter device, in that the diameter of the tubular housing is widened at its end areas more or less in the manner of a sleeve, these widened areas being provided with radial connection pieces. These connection pieces open through into the second space formed by the housing, the widened sections of the housing being sealed off from the first space because the caps are sealingly joined to the widened sections, so that a sealing is produced to the outside by the cap edge, and a sealing is produced with respect to the first space by the circumferential sealing ring. This type of arrangement of the connection pieces at the second space formed by the housing is relatively costly. Furthermore, dead spaces which are poorly rinsed develop above or below the connection pieces, at which gas bubbles can collect. This can have a disadvantageous effect during disinfecting or sterilization, as well as generally when handling.
Therefore, the object of the invention is to produce a filter device of the type specified at the outset in which, on one hand, it is reliably assured that the two flow spaces are sealed off from one another by the hardened molding compounds, and on the other hand, a simple arrangement of the connection pieces for the second flow space is produced and poorly rinsed dead spaces are moreover avoided.
This objective is achieved according to the invention, given a filter device having two flow spaces, the first space formed by tubular or capillary tube passages of a hollow-fiber bundle, said fiber bundle being poured at its ends into a molding compound, and a second space formed by the housing surrounding the fiber bundle. The invention further entails the first space being sealed off by caps, placed on the molding compounds, with sealing devices being placed over the peripheral areas of the molding compounds, and the molding compounds being braced against the housing. The molding compounds are hardened in molds enclosing them at their end faces and peripheral sides to form disks. Caps are provided for the ends of the first space that seal to the molding compound and have a connection piece providing inflow/outflow access to the first space. A second set of caps, overlapping the first caps, is provided, said caps having a connection piece providing inflow/outflow access to the second space. The edges of the second caps being joined to the housing in a fluid tight manner, so that between the first and second set of caps, interspaces are formed, said interspaces being connected to the second space.
In the filter device according to the invention, the molding compounds are hardened in molds enclosing them on the face and at their sides, so that the molding compounds are able to shrink free of stress. As in the known filter device, the sealing between the disk-shaped molding compounds thus formed and the first caps is effected by inserted sealing means. However, to produce a simple access to the second flow space, the corresponding connection pieces are no longer arranged on the housing itself, but on the second cap overlapping the first cap. This simplifies the filter device.
The inner edges of the second caps overlapping the molding compounds advantageously extend beyond the molding compounds to the inside, so that a flow space is produced between the circumferential wall of the second caps and the molding compounds or the fiber bundles enclosed by them.
According to a preferred specific embodiment, the pipe-section-shaped housing, into which the hollow-fiber bundle is drawn, is provided at the ends of its casing with tooth-like or scalloped projections formed by axial notches or indentations running out freely, the outer areas of the projections being integrated into the molding compounds, so that the free inner areas of the notches or indentations form flow passages for the fluid. Since the housing, which is pipe-section-shaped or preferably provided with a circular cross-section, is made of a material having elastic properties such as PC (polycarbonate), wreath-shaped edges made of flexible tongues are formed by the notches or indentations, said edges being at least partially enclosed by the molding compound. When the molding compound then hardens to form the disks, they can shrink essentially free of stress, because the flexible tongues offer no significant resistance to this shrinking. According to this refinement of the present invention, the disks formed by the molding compounds are firmly joined to the ends of the tubular housing, so that the two flow chambers can then be reliably separated from one another by the two caps overlapping one another, with the appropriate sealing means.
It may be that the filter device known from EP 0 305 387 B1 has a tubular housing, in which wreath-shaped edges formed by notches or indentations are produced in the widened end sections and are partially enclosed by the molding compounds hardened to form disks. However, these wreath-shaped edges made of rectangular projections demand a complicated design of the housing, because in addition, they are still enclosed by the widened end sections of the housing which are provided with the connection pieces.
The housing is expediently provided in the area of the inner ends of the projections with radial flanges, on which the edges of the second caps are sealingly supported, or to which they are secured.
Advantageously, the distance of the projections from one another in the circumferential direction is greater than their width.
According to one inventive embodiment, for which independent protection is claimed, the cross-sectional area of the regions of the notches or indentations free of the molding compounds is so dimensioned that, starting from a radial connection piece, they increase in their cross-section, so that essentially equal partial quantities of the fluid can enter and exit through the cross-sections. This embodiment takes into account the circumstance that, in the annular space surrounding the fiber bundle and into which the liquid is fed through a radial connection piece, a pressure drop occurs in the circumferential direction starting from the mouth of the connection piece. Adjusting the cross-sections of the intake ports to this pressure drop assures that essentially equal quantities of fluid enter the openings distributed over the circumference.
A special problem in filter devices of the type indicated at the outset is assuring that in the second space, the surfaces of the fibers in the hollow-fiber bundle are circumflowed as completely and uniformly as possible by the introduced fluid, in order to increase the effectiveness of the filter device. Therefore, according to one particularly preferred specific embodiment of the invention, inserted into the housing are saucer-shaped rings whose legs are joined to the inside wall of the housing and which are provided with bore holes, and that the inside wall is provided with bore holes opening through into the annular spaces formed by the rings. An annular space is formed by the saucer-shaped ring, in which the introduced fluid can spread out well. The bore holes can be distributed uniformly over the periphery, in doing which the cross-sections of the bore holes can be adapted to the pressure drop occurring in the introduced fluid if it is fed into the annular space only through one bore hole or one radial connection piece.
To maintain an essentially uniform fluid pressure given a one-sided introduction of the fluid into the annular space, the bore holes and openings respectively having identical flow-through cross-sections can be distributed with appropriately variable clearances over the periphery of the inside wall of the annular space.
Advantageously, the rings have a U-shaped cross-section, the bore holes being arranged in the radial legs of the rings.
In the known filter device, the annular spaces formed by the annular grooves have an axial clearance with respect to the end disks formed by the molding compounds. Because of this, in the case of a vertically standing filter device, for example, air bubbles can collect at the upper disk formed by the molding compound. Furthermore, air bubbles can also collect in the lower annular groove between the mouth of the radial connection piece and the groove bottom. A result of this undesired collecting of air or air bubbles is that, for example, during sterilization or disinfection of the filter, the air-filled areas do not come in contact, or come only insufficiently in contact with the sterilizing or disinfecting means.
To achieve a complete deaeration of the hollow-fiber space, a further inventive development provides that the annular spaces or the passages connecting the annular spaces to the second space are joined directly to the molding compounds, or extend in the axial direction to their area.
This refinement of the present invention prevents dead spaces between the connection pieces and the annular spaces respectively into which they discharge, so that no air can accumulate in unwanted manner in dead spaces, and a complete circumcirculation of the hollow-fiber bundle by the fluid between the molding compounds is assured.
Expediently, both sides of the filter are identically shaped, so that the effects provided according to the invention are attainable in any position of the filter.
The embodiment of the filter according to the invention also has a favorable effect on the discharge side of the second space, since the fluid is withdrawn from the second space essentially uniformly distributed over the annular space.
A further advantage of the present device is that its housing can be made of a material such as propylene which does not form a tight adhesive bond with the molding compound. Therefore, it is possible to produce the filter device according to the invention from less costly plastic materials, which increases its economic efficiency.
A further inventive refinement relates to a filter device having two flow spaces, of which a first space, preferably a permeate space, is formed by the tubular or capillary tube passages of a hollow-fiber bundle poured at its ends into a molding compound, and a second space, preferably a filtrate space, is formed by a housing enclosing the hollow-fiber bundle. The filtrate space is sealed off from the inlets and outlets of the tubes of the hollow-fiber bundle by the molding compound. Furthermore, at least two connection pieces are provided for the feeding and removal of fluids into or out of each of the two spaces, of which at least one connection piece of the second space opens through into an annular space formed between the housing and the area of one end of the hollow-fiber bundle. To assure that there is no dead space in the annular space in which air bubbles can collect, the present invention provides that in the position of normal use, at least one annular space is located at the top, and that the annular space extends to the supply line and discharge line respectively. Preferably dialysate can be fed or removed through the upper annular space.
In the following, an exemplary embodiment of the invention is explained in more detail with the aid of the drawings.